<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        body {
            width: 100%;
            position: relative;
        }

        .left {
            width: 100px;
            height: 150px;
            float: left;
            background: rgb(139, 214, 78);
            text-align: center;
            line-height: 150px;
            font-size: 20px;
        }

        .right {
            height: 300px;
            background: rgb(170, 54, 236);
            text-align: center;
            line-height: 300px;
            font-size: 40px;
        }
    </style>
</head>
<body>
<div class="left">LEFT</div>
<div class="right">RIGHT</div>
</body>
</html>